Benign prostatic hyperplasia is a progressive condition in the aging men characterized by the enlargement of the periurethral regions of prostate gland due to nonmalignant proliferations in both the prostate epithelial and stromal compartments. An estimated 50% of men have histologic evidence of BPH by age 50 years and 75% by age 80 years. BPH is often accompanied by lower urinary tract symptoms (LUTS). BPH is rarely fatal, but may cause serious life-threatening complications such as acute urinary retention if left untreated. Androgen targeted therapies such as finasteride are clinically employed for the treatment of BPH. However, the MTOPS study shows that even combination therapy using finasteride and doxazosin only leads to a 66% reduction of risk for clinical progression of LUTS/BPH, suggesting the existence of unrecognized mechanisms that promote disease progression. The goal of this application is to investigate novel molecular mechanisms that contribute to BPH initiation and progression. This application is based on our novel preliminary observation that attenuating the androgen receptor signaling in prostate epithelial cells induces an inflammatory microenvironment. We hypothesize that this prostatic inflammatory microenvironment contributes to progression of BPH. Through the three Aims in this application, we seek to generate novel mouse models for human BPH, use mouse models to determine the contribution of immune cells to prostate epithelial cell proliferation, and identiy novel key signaling mediated by the inflammatory prostatic microenvironment that is capable of promoting epithelial cell proliferation.